A body structure of a vehicle includes a pair of side sills, positioned on the right side and left side of the vehicle, seat cross-members extending between the side sills, and a floor pan extending beneath the seat cross-members between the side sills. The seat cross-members are welded to the side sills and are welded to the floor pan. The floor pan is welded to the side sills. A weld span without welds between the side sills and the floor pan exist along the seat cross-members. In other words, the seat cross-members restrict access to the interface between the side sills and the floor pan along the seat cross-members, such that no welds are made between the side sills and the floor pan along the seat cross-members. This weld span without welds along the seat cross-members may be between 165-185 mm.
During vehicle crash testing, e.g., small offset rigid barrier tests, side impact tests, etc., the welds between the floor pan and the side sills are subjected to forces. The welds between the floor pan and the side sills adjacent the seat cross-members may be subjected to the highest forces and, as such, a higher opportunity for separation between the floor pan and the side sills may occur in this area during crash testing. When the side sills and the seat cross-members are formed of mild steel, the mild steel may be stamped and trimmed in ways to increase the interaction and welds between the side sills and the floor pan in the area of the seat cross-members to reduce the possibility of separation between the floor pan and the side sills during crash testing.
High strength steels are being used increasingly in the formation of the side sills and the seat cross-members. The material characteristics of the high strength steel allows the side sills and the floor pan formed of high strength steel to be thinner, i.e., lower gage, than the same side sills and floor pan made from mild steel. As such, the use of high strength steel allows for the side sills and floor pan to be made thinner, and thus lighter, to aid in improving fuel economy of the vehicle. However, high strength steel is less workable than mild steel. As such, there remains an opportunity to design a body structure having side sills and seat cross-members formed of high strength steel and that reduces the possibility of separation between the floor pan and the side sills during crash testing.